Apparatus for transforming halftone documents into a printing weft



Oct. 3, 1950 LANGE 2,524,531

' APPARATUS FOR TRANSFORMING HALFTONE DOCUMENTS INTO A PRINTING WEFTFiled May 7. 1947 4 Sheets-Sheet 1 GE ORMING HAL Get. 3, 1950 M. LAN2,524,531

APPARATUS FOR TRANSF FTONE DOCUMENTS INTO A PRINTING WEFT 4 Sheets-Sheet2 Filed. May '7. 1947 Oct. 3, 1950 M. LANGE APPARATUS FOR TRANSFORMINGHALFTONE DOCUMENTS INTO A PRINTING WEFT Filed Nay 7. 1947 4 Sheets-Sheet3 m 4 a U .z gyvenlbr L g 9% 2 HZZQYLYS Oct. 3, 1950 I M. LANGE2,524,531 APPARATUS FOR TRANSFORMING HALFTONE DOCUMENTS INTO A PRINTINGWEFT Filed May 7. 1947 4 Sheets-Sheet 4 7. La/ qe Patented Oct. 3, 1950APPARATUS FOR TRANSFORMING HALF- TUNE DOCUMENTS INTO WEFT A PRINTINGMaurice Lange, Issy-les-Moulineaux, France, assignor to EtablissementsEdouard Belin, Rueil- Malmaison, France, a corporation of FranceApplication May 7, 1947, Serial No. 746,442 In France May 8, 1946 4Claims.

The invention has for its object to provide a process and an apparatusmaking it possible to obtain automatically and with high speed ascreened or hatched reproduction, either on a film or on any otherphotosensitive surface, of an original document in outline or in halftone.

The process and apparatus according to the invention may in particularbe used for obtaining engraved surfaces designed for printing onfabrics.

The engraving of such surfaces involves hatches wherein the spacing orpitch and the ratio between the sunk and solid area are varied with theintensity of the tint to be reproduced; said hatches simply providemeans to retain a more or less large amount of ink, which, beingdistributed in the fibres of the fabric, reproduces the fiat or shadedtones of each one of the tints in the original drawing.

The method of the invention is characterized .by the following sequenceof operations:

The original image is analyzed or scanned by A fixed luminous beam ofconstant intensity v is created and is caused to be reflected from themirror controlled by the analyzing device,

:so that the reflected beam or pencil of light .occupies a positionwhich at any instant is a function of the tint analyzed upon theoriginal document.

The reflected pencil of light is periodically intercepted and during theperiods where it is not so cut off it acts on the photosensitive surfaceeither directly or through the medium of a special device which iscontrolled by it, and in such a way that there is obtained on thephotosensitive surface a pattern corresponding to the design to bereproduced.

In a modification of the process, the periodically intercepted pencil oflight is caused to act on a device controlling an engraving tool orpunch thereby making it possible directly to obtain an engraved surface.

The apparatus according to the invention comprises in combination:

A device of known type to analyze or scan the original image, whichdevice at each instant determines the angular orientation of a mirror asa function of the tint at the point analyzed at that instant;

A device for periodically intercepting a luminous pencil refiected fromthe above-said movable and an amplifier a mechanical or electricaldevice actuating an engraving tool or punch directly engaging thecylinder to be engraved.

The method of the invention is operated by means of an apparatus whereofthe accompanying drawings diagrammatically illustrate two embodiments byway of indication only and without in any way limiting the scope of theinvention.

Fig. 1 shows an enlarged view of one specific form of screen pattern.

Fig. 2 shows a form of disk providing for the periodic interception ofthe pencil of reflected light which at each passage thereof determinesthe recording of one element of the screen pattern.

Fig. 3 shows a screen provided with a triangular aperture therein andplaced in front of the intercepting disk between the latter and thereflected pencil of light.

Fig. 4 is a diagram showing a screening apparatus cooperating with adisk and a screen such as shown in Figs. 2 and 3.

Fig. 5 is a view partly broken away of another type of disk comprisingrings of radially extending slots.

Fig. 6 shows a portion of the disk and the slotted screen covering thesame for one particular position of the principle and secondary spotsobtained with the screening assembly or stand of Fig. 10.

Fig. 7 shows a portion of the radially slotted disk and the screencovering it when the main luminous spot is positioned at the boundary ofthe slots of one ring of slots.

Fig. 8 shows a position of the secondary spot corresponding to thescreening assembly or stand of Fig. 10 at the passage f the main spotfrom one ring of slots to the adjacent ring of slots.

Fig. 9 shows one specific form of the large triangular slot of thescreen placed in front of the disk.

Fig. shows a diagram of the layout of a screening assembly or stand witha disk comprising rings of slots.

As shown in Fig. 4 an oscillograph or more generally a galvanometerincluding a mirror M is actuated by the analyzing device analyzing theoriginal document to be reproduced, which analyzing device may be suchas are used in phototelegraph transmitter equipment of any known type.

The mirror M is movable about an axis perpendicular to the plane of thefigure; it is illuminated by a lantern comprising a source of light A, acondenser L, an arcuate slot F and an objective lens L adapted to formupon the mirror M the image of the luminous source A.

The mirror M reflects a pencil of light which finally forms a spot orimage S of the slot F on a screen G (see Fig. 3) formed with atriangular aperture H. The expression triangular aperture is used todesignate an aperture having a generally triangular outline but thesides of which may be either rectilinear, curved or more or less brokenr irregular.

A disk D is disposed against the screen G; said disk D which is movableabout its center 0 is provided with slots such as J or perforations K ortransparent portions corresponding to such apertures or perforationswhich ride in front of the aperture H of the screen G as the disk Drevolves.

The disk D is driven in rotation from an electric motor or an equivalentdevice; said disk may be made of any suitable opaque material whereinslots or perforations are cut out or may be constituted by aphotographic film wherein the slots or perforations may appear bytransparency.

Behind the disk D is arranged an aplanatic converging lens L adapted toconcentrate the light of the narrow-beam or pencil passing through thetriangular slot. H and one of. the slots in the disk D upon aphoto-electric cell C.

As the disk D rotates the photo-electric cell C therefore receives asuccession of luminous signals; said photo cell C is connected with theamplifier E or any suitable conventional type the output of whichprovides a current whereof the magnitude may thus assume one of twopredetermined values, the one corresponding to dark ness and the otherto illumination as the pencil traverses any one of the apertures in thedisk D.

The output current from the amplifier E is (when necessar after havingbeen rectified) conveyed to a receiver device R. which comprises anoscillograph the mirror of which oscillates when said oscillograph istraversed by the variable current from the output f the amplifier E.Said mirror is illuminated b a luminous source through an optical systemand provides upon a slotted screen a movable image or spot; when thisspot falls upon a slot in the screen the pencil of light traverses anoptical system adapted to form a light spot upon the photo-sensitivesurface of the recording or reproducing cylinder B.

The disk D may be formed with slots in widely varying dispositions orpatterns.

In the case of Fig. 2 said disk D has drawn thereon a number ofequi-spaced circumferences a, b, c, d, n, eight in number for example.The innermost circumference a is subdivided, starting from the uppervertical diameter, into Nequal portions, 12 in the instant case, thecircumference b is divided into N+l portions, i. e. 13, thecircumference 0 will include N+2, i. e. 14 portions, etc, that is thenumber of divisions is increased by one digit from any one circumferenceto the next larger one. The slots and perforations are formed throughthose points of subdivision and in such a way that, were the spot S tofall through the slot H onto the circumference a, it would provide, ateach revolution of the disk, 12 luminous signals on the cell C whereasupon the circumference b it would give 13 signals; the number of saidluminous signals being regularly increased by one digit as the spot s isdisplaced outwardly of the disk.

The disk D of the type shown in Fig. 5 is of much simpler construction;it comprises rings of radical slots J starting from equi-spacedcircumferences a, b, c, d, each respectively comprising 14, 18, 24 and28 slots of equal height.

In other words, the variation in the number of luminous signalstransmitted through said disk D towards the photo-cell C for eachrevolution of the disk is discontinuous as the spot passes from theinnermost circumference a to the outermost circumference b.

The screen G used with the disk D comprising radial slots furtherincludes three additional rectangular slots I, I, I", and the Screen ofthe lantern is in this case provided with an additional slot F whichforms upon the screen G after reilection from the mirror M of theoscillograph a second light spot S.

Whenever said light spot S passes through one of the slots I, I, I" itis picked up by the aplanatic lens L", then by a total reflection prismP which directs the light pencil back upon a photo-electric cell C". Thedirect current output of the cell C, as amplified by a tube E having ahigh-slope amplifying characteristic is fed back into the circuit of theoscillograph actuating the mirror M.

Said oscillograph circuit normally receives the output current from themodulating amplifier controlled by the photo-cell Which scans theoriginal document and the current generated by the secondary photo-cellC is thus added to the normal current.

The stepped form of the slot I-I (Fig. 5) is desirable in the case of aflat-tint document, that is such as does not comprise continuouslyshaded tints; the aperture H has as many steps as there are ringsof-radial slots in the disk D.

The screened pattern obtained through the use of a disk such as D (Fig.2) enabling the number of luminous signals to be varied in a continuousor progressive manner is constituted by rectangular elements (sunk andsolid areas) of constant width, variable in length and also in pitch orspacing p (Fig. l) The spacing 6 between the rows of rectangularelements may be totally suppressed so that the merging-of saidrectangular elements will determine the production of hatches.

When there is used the disk D of the type involving a continuousvariation in the number of light signals and starting from a designdrawn in Indian ink comprising shaded or Washed tints, the apparatusoperates as follows:

The document to be screened is spread over a cylinder which isphoto-electrically scanned just as if it were desired to transmit aphotograph over a telephotograph system; the modulated current outputof-the amplifier is fed to a galvanometer such as an oscillograph placedupon the screening stand.

The light spot S directed from the mirror M of said oscillographimpinges on the screen G formed with the triangular aperture H and whichis arranged in front of the disk D, the axis at y of the triangle I-Ilying in a vertical plane passing through the axis of rotation 0 of thedisk, and its base being level with the circumference a, while its apexis level with the circumference n. The displacement of the mirror M isadjusted so that the spot will start from the base of the triangle for adark area of the original document and will rise towards the apex ofsaid triangle for the lighter shades of grey. Pure white will cause thespot to be projected beyond the apex of the triangle, because it then isunnecessary to screen it.

Assume by way of example that the circumference a has been divided into12 portions and the outermost circumference 12 into 19 portions. Thebase of the triangle H which is structurally arranged to be positionedin front of the innermost circumference a comprising twelve aperturesper revolution will therefore allow the spot of light to pass twelvetimes per revolution of the disk, each time said spot impinges on thatpoint. The apex of the triangle H positioned in front of the outermostcircumference which includes nineteen apertures per revolution willallow the spot to pass nineteen times per revolution. Any intermediateposition will correspond to successive on and off conditions of thelight spot in a number comprised between twelve and nineteen. It followsthen that a black area of the document will be hatched twelve times andthe intermediate tints will be hatched a number of times included in therange of from twelve to nineteen. At each passing of the aperture,photo-cell C (or the cylinder B as the case may be) will be struck byaluminous signal of constant intensity but the duration of which is afunction of the position of the spot upon the triangle H. It is obviousthat when the spot impinges on a point located towards the base of thetriangle the duration of the signal is greater than when it falls upon apoint near the apex.

The process forming the subject of the invention presents a remarkableflexibility inasmuch as it is simply necessary to modify the contour ofthe triangle H in order to shorten or lengthen the duration of thesignals. There is thus provided a simple and practical means tocompensate or correct certain shadings, and the sides of the trianglemay be provided with curved or broken lines restricting the length ofthe signals.

Also it is sufficient to adjust the length of the stroke and theposition of the spot on the triangle to transmit the shading with a moreor less great number of points. Such number of points will be determinedby the quality and thickness of the material to be ultimately printed.

The electric signals supplied from the output of the amplifier of thephoto-electric cell on the screening stand (see Fig. 4) are directedtowards the device R controlling recording on the cylinder B orreproducing cylinder housed in a lighttight box and which may forexample be mounted on the same shaft as the cylinder supporting theoriginal document, which in this particular instant will ensure positivesynchronism of operation without the provision of any special means.

If the apparatus is devised in such a manner that, structurally, eachrevolution of the disk B will correspond to a linear displacement of onecentimetre when the disk transmits twelve signals per revolution, it maybe said that the screen pattern comprises twelve points per centimetre.

If the disk transmits nineteen points, the screen will be said to havenineteen points per centimetre and so on,

The rates of rotation of the cylinder and the driving motor for the diskD may be electrically interlinked by being electrically in step witheach other to enable an accurate definition of the number of points percentimetre to be obtained.

The disk D comprising a ring of radial slots (Fig. 5) is used in anumber of cases where a continuous or progressive variation in the pitchstep is unnecessary, and where a limited number of different screenpatterns is suflicient to give a shades impression, because the trianglecut out in the screen, which is positioned in front of the disk, alreadyhas for its function to thicken or conversely to reduce the length ofthe luminous points impressing the photographic film placed on therecording cylinder.

A screened document may for example be formed by four different kinds ofhatches. By way of indication, fourteen hatches per centimetre maybe'used for background tints, eighteen for dark tints, twenty-four formedium tints and twenty-four for pale tints. Naturally the above figuresare given merely by way of indication and the number of hatches as wellas their pitch step or spacing may be varied according to the nature ofthe support to be printed and also the composition of the colour whichis to be used or the effect to be provided.

The disk D may for instance comprise, starting from the circumference,a, b, c, d, four rings of slots of similar height, the first ring havingfourteen slots, the second ring eighteen, the third twenty-four and thefourth twenty-eight,

It will be seen that the spot S may be so positioned as to overlap theslots of two successive rings, for instance the second and third ringsb, c, and in this position there would be 18+24 luminous signalstransmitted.

It is therefore necessary to provide means such that the spot S will beincapable of occupying such a position and will pass suddenly from onering to the next one.

The mirror M of the oscillograph (Fig. 10) is adjusted so that the spotS will be positioned over the aperture H (Fig. 6) in the total absenceof any current (white areas) and at the base of said aperture when thereis a maximum current (black areas).

When said current passes from a minimum to a maximum the spot S occupiespositions intermediate between the apex and the base of the aperture H.

Assume the original document is in one color drawn in Indian ink inshaded tints. If a given shade or tint causes the main spot S (see Fig.6) to be stopped upon the ring of slots b, that particular tint beingshaded, thespot will move along that ring of slots.

The spot S isstructurally positioned at a certain distance from theaperture I. The photocell C (Fig. 10) or the film will record theluminous impulses provided by the spot S through the aperture H and theslots of the ring of slots b. The duration of said impulses will beproportional to the width 1 of the triangle (Fig. 6) at the place wherethe spot passes therethrough since any one of the slots of the ring brequires a period of time t to travel over the distance1.

If the shade becomes darker, the main spot S (Fig. 6) moves downwardsand the secondary spot S moves with it because they are both controlledby the mirror of the oscillograph. When the main spot is-at the baseofthe ring of -slo'ts'b (Fig, '7) the width "1'" of the triangle at thispoint is greater than 1. Because .the screen pattern has not changedthere will be the same number of luminous impulses per centimetre ofcylinder travel, but the duration of each impuise will be greatersince-each slot of the ring requires more time to travel through 1' thanit d-i'd to traverse l, and the net result will be that there will bemore colour deposited upon printing.

For this position of the main spot S,the secondary spot S willhave movedcloser tothe aperture I to the point of touching it, but should bothspots continue to move downwards by a few tenths of a millimetrefurther, that is should the spot S tend to move towards the ring ofslots a, the light from the secondary spot S would begin to pass throughthe aperture I, the photo-cell C is slightly illuminated and generates asmall amount of current which is fed back tothe oscillograph, the mirrorM of which causes the spots S and S to move still further down. The spot.8 passes through the aperture I to a greater eX- tent, and there istherefore an increase in the current supplied to the oscillograph. Thespots S and S will thus move further down and so on, until S is allowedto completely pass through the aperture I. The spot S is then positionedat the upper part of the ring of slots 0.. At that time a state ofbalance sets in, becauseif the spot S were to move down any further, itwould move out of the slot I and the photo-cell being less stronglyilluminated would generate less current which in turn would cause thespots to move upwards.

The above-described movement is effected V31; rapidly and the main spotS jumps very fast from one ring of slots to a next one without beingallowed to stop 'astride a pair of differentrings.

, After the spot S has reached the position illustrated in Fig. 8, oneof the following two conditions may occur:

1. If, as a' result of a change in shading in the document, the spots 'Sand S have a. tendency to rise, the secondary spot S will no longerentirely pass through the aperture I, and thephoto-cell C shown in Fig.10 will supply less current to the oscillograph. As a result the spots Sand S will rise yet further and the cell C will receive less and lesslight until it remains completely in the dark and the spots S and S willagain be restored to the position of Fig. '7.

2. If on the other hand the shading of document being scanned is such asto cause the spots S and S to move down rather than up, the secondaryspot S will move away from the aperture I. the photo-cell C of Fig. 10will receive less light thus feeding less current to the oscillographwhich in turn will be effective to retard the downward movement of thespots. This is manifested by a slight flattening in the modulation whichwill prevail as long as the secondary the spot S has not entirely leftthe aperture I.

In the case of fiat-tinted documents and with the stepped form ofaperture H (Fig. 9),

the operation of the light spots will be the same as previouslydescribed; but the displacements of the main spot S over a given ring ofslots provide on the main cell C of Fig. 10 periods of illumination ofequal duration. Said displacements being simply'due to the slightirregularities which may occur in the flat tint corresponding to thatparticular ring of slots, correction is therefore automaticallyeffected. The spot s moves from one ring to another only when there isachange in the shade of the flat tint.

The=displacement of the mirror of the oscillograph with respect to thecurrent fed to the latter is generally not strictly proportional to saidcurrent.

It follows that if it is desired always to obtain a similar displacementfor the spot S as it jumps from the ring a to the ring I), then from bto c and later from c to d, the three apertures I, I, I should not beidentical. Their height dimension is left unchanged, but, in the case ofFig. 7 for instance, the slot I will be provided longer than I which inturn will be longer than I. In other words, to obtain a similardisplacement for the spot S, it is necessary that the photo-cell shouldreceive lIlOlE light when the spot S is positioned towards the base ofthe aperture H than when S is positioned towards the top. The lengthdimensions for I, I and I" are determined experimentally once for allaccording to the type of oscillograph used.

It will of course be understood that various alterations, improvementsand additions may be made in the embodiments described and illustratedand certain devices therein may be replaced by equivalent ones withoutthe general principle of the invention being thereby altered.

Thus in particular the rings of slots may be provided with varyingheights if required, in the case of flat tints; the location of theadditional slots and the secondary spot on the screen may diner fromthat shown, as for example it may be at one side of said screen.

As previously stated, the intermittent luminous signals produced fromthe pencil of light issuing from the source of light A through the slotF after reflection from the mirror M and through the screen G, disk Dand lens L may if desired be caused directly to engage the reproducingcylinder B.

Finally any mechanical or electrical device controlling an engravingtool or punch may be operated from the amplifier of the main photocell;also, the optical device controlled from the same amplifier and actingon the same photocell may be of any suitable type.

What I claim is:

1. A reproducing arrangement for transforming half-tone documents into aprinting weft, of tne'type wherein the document to be transformed isscanned by photoelectric means and wherein a light beam reflected by agalvanometer mirror responsive to the electrical current from saidscanning means passes through slots in a rotating obturator disc and iscaused to sweep said disc from the center to the periphery thereof inaccordance with the shade of the scanned area in the document, whereinsaid slots are regularly spaced angularly along circumferences coaxialwith said disc with a number of said slots varying from the center tothe periphery of said disc, and said reflected light beam passes througha fixed, substantially triangular aperture arranged in the vicinity ofsaid disc and whose main axis extends radially with respect to said discwith its base in regard to that portion of said disc provided with thelesser amount of said slots, whereby light signals are produced whosenumber and cross-sectional area at any time are functions of the shadeof the area scanned at that time in said document.

2. A reproducing arrangement as set forth in claim 1, wherein said slotsare of constant width throughout and extend along a curved path in ageneral direction from the center to the periphery of said obturatordisc, the number of said slots progressively increasing from said centerto said outer periphery and the interspacing of said slots, as measuredalong circles coaxial with said disc, being constant along any given oneof said circles.

3. A reproducing arrangement for transforming half-tone documents into aprinting weft of the type in which the document to be transformed isscanned by photoelectric means and in which a light beam reflected bythe mirror of an oscilloscope having a galvanometer responsive to theelectrical currents from said photoelectric scanning means passesthrough slots in a rotating obturator disc and is caused to sweep saiddisc from the center to the periphery thereof in accordance with theshade of the scanned area in said document, comprising in combination:an axis about which said mirror is adapted to swing; means for strikingsaid mirror with a pair of light beams of constant intensity therebyforming a pair of separate reflected light beams the angular spacing of.which remains constant; a screen in the path of both said reflectedlight beams, formed with a substantially triangular aperture therein inthe path of a first one of said reflected light beams, the main axis ofsaid aperture being perpendicular to said swinging axis, said screenfurther being formed with a plurality of slits each extending in adirection parallel to the direction of said first-mentioned axis, saidslits being arranged in the direction of said main axis for said.triangular aperture in the path of the second one of said reflectedlight beams; said slots in said obturator disc being distributed inseries of slots having a constant circumferential width and regularlyspaced along circumferences coaxial with said disc, the number of theslots in each of said series increasing from a central circumference toan outer circumference, and the number of said series of slots beinggreater by one digit than the number of said slits in said screen; saidobturator disc being positioned beyond said substantially triangularaperture with respect to said mirror with a radius parallel to said mainaxis of said aperture and with the base of said aperture lying in regardto the central portion of said disc; second photoelectric means adaptedto be struck by said second reflected light beam when passing throughany one of said slits; means for connecting said second photoelectricmeans with said galvanometer thereby imparting to the same an additionalangular displacement; and said slits in said screen and said series ofslots in said obturator disc being so positioned with respect to eachother that said second reflected beam only completely sweeps a relatedone of said slits when said first reflected beam impinges on saidobturator disc substantially between two radially consecutive series ofslots, whereby the additional angular displacement imparted to saidmirror through said second photoelectric means at any time insures thatsaid first reflected light beam only rests on an annular area of saidobturator disc provided with a related series of circumferential slots.

4. In a reproducing arrangement as in claim 3, said substantiallytriangular aperture in said screen being formed with stepped lateraledges whose straight portions are arranged respectively in front of saiddisc circumferences provided with said series of slots.

MAURICE LANGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,980,150 Baird Nov. 6, 19342,063,998 Gray Dec. 15, 1936 2,152,348 Finch Mar. 28, 1937 2,274,841Mathes Mar. 3, 1942 2,287,033 Goldmark June 23, 1942 2,294,643 WurzburgSept. 1, 1942 2,347,015 Woloschak Apr. 18, 1944 2,357,938 Dench Sept.12, 1944 2,432,123 Potter Dec. 9, 1947 FOREIGN PATENTS Number CountryDate 294,508 Great Britain July 16, 1928

